How would the story ever move forward if it is constantly going back in time? It worked well in IV because they were DLC, but we're talking about the exact same timeline playing over and over again. Why would you want to do all of these things as one character and then get thrust back to the beginning as someone else?
I'm not saying the stories shouldn't - all of them will be about chasing the dollar, as we already know - but do you not think it would be amazing if say the first character was to die at the end of his story, and then it cuts and you play as the man who killed him? There would be no point if it keeps going back in time, as the endings to each story would just be repetitive with no hint at the story developing beyond that point.
It's hard to get across what I am thinking. Imagine it more like LCS or VCS as opposed to TLAD or TBoGT - the stories still overlap and compliment each other without being played in the same timeline as the originals.